To get anywhere at all, we will have to hew out rough models of interaction among groups, and of a single group’s collective action. At first chop, the model of interaction is quite static. Let us call it our polity model. Its elements are a population, a government, one or more contenders, a polity, and one or more coalitions. We define a population of interest to us by any means we please. Within that population we search for one or more of the following:

Government: an organization which controls the principal concentrated means of coercion within the population.

Contender: any group which, during some specified period, applies pooled resources to influence the government. Contenders include challengers and members of the polity. A member is any contender which has routine, low-cost access to resources controlled by the government; a challenger is any other contender.

Polity: consists of the collective action of the members and the government.

Coalition: a tendency of a set of contenders and/or governments to coordinate their collective action.